The invention relates to providing bi-directional broadband data services over resource-sharing networks using distributed local access control.
Communication networks can be divided into two major categories: (a) central-control and (b) peer-to-peer. The central-control networks deploy a central office (CO) to control all the transmissions to and from end users (EUs). In peer-to-peer networks, the EUs control their own transmission in coordination with other EUs with or without the help of the CO.
a. Central Control Systems
Central control systems could be either point-to-multipoint systems, such as passive optical networks (PONS) and hybrid fiber/coax (HFC) networks, or point-to-point systems, such as active star networks (ASN) used in current local telephone systems.
In point-to-multipoint systems, multiple users share the same physical transmission media. For downstream transmission, information is broadcast to all or groups of users over the downstream channel(s) and each EU selects the information addressed to this particular user. For upstream transmission, Time Division Multiple Access (TDMA) is one of the methods often used to avoid collision over the shared transmission path. Using TDMA, in which multiple EUs share the same frequency or wavelength channel, certain media access control (MAC) has to be deployed at both CO and EUs to coordinate the traffic and let the EUs access the same channel in turn.
Reservation-like or reservation-contention combined MAC protocol is usually used, in which the CO either preschedules all the EUs"" upstream transmission or dynamically assigns the upstream channel (time slot) for each EU based on its request.
Several difficulties or complexities arise with these point-to-multipoint systems using the aforementioned protocol. Because the distance from the CO to each EU is different, the MAC protocol has to be able to resolve problems arising as a result of the different distances. Delay and overhead in transmission are therefore unavoidable. Further, in systems like conventional HFC, the limited upstream bandwidth and noise also make it necessary to use certain modulation schemes such as quadranture phase shift keying (QPSK) or quadranture amplitude modulation (QAM) techniques, because they are bandwidth efficient and robust to noise. However, these systems are also complicated and expensive.
In point-to-point systems, the CO has dedicated physical lines to each EU. Therefore, no MAC is needed. However, the implementation and maintenance could be very expensive. Some systems deploy remote nodes which perform the concentration or multiplexing function to achieve equipment sharing, thus reducing the cost (Active Double Star: ADS; Fiber-to-the-curb: FTTC). Nevertheless, the remote nodes could become a potential bandwidth bottleneck for future capacity requirement.
b. Peer-to-peer Systems
Peer-to-peer systems are very popular in computer networks, especially in Local Area Networks (LANs). In these systems, each EU controls its own transmission in coordination with other EUs with or without the assistance of the CO. The MAC algorithm could be contention or reservation-based Aloha, Carrier-Sense Multiple Access with Collision Detection (CSMA/CD), or token pass, which are all protocols well known in the art. The most widely used LAN is the Ethernet using CSMA/CD protocol.
Based on the CSMA/CD protocol, each EU listens to the traffic before transmitting (carrier-sense), transmits as soon as channel is idle, stops as soon as collision is detected (collision detection), and retransmits after back-off (the user defers transmission for a certain time period based on certain algorithms). The network is therefore self-controlled or self managed.
Because all the users share the same logical path for bidirectional transmission which is broadcast to the entire network, when one user is talking all the other users have to listen. Therefore, only half-duplex transmission can be achieved. This method is suitable for local area communication under low-load conditions, and allows only a small amount of traffic from the outside world to be efficiently transmitted into the LAN. It also requires that each EU detect collisions before finishing sending the packet. Therefore, the round trip delay over the entire network needs to be shorter than the time necessary to transmit an Ethernet packet having minimum packet size (512 bits or 51.2 xcexcs at 10 Mbps). This limits the transmission distance to only a few kilometers. In addition, the broadcasting scheme also gives EUs no privacy because they are required to listen to other EUs"" transmission.
Compared to the reservation-based MAC protocol used in central control networks, the contention-based CSMA/CD has the advantages of simplicity, low delay and less overhead at light traffic load, and no CO is necessary to coordinate the traffic. However, its local-broadcasting nature with limited transmission range and half-duplex operation makes it unsuitable for applications beyond LANs.
On the other hand, the directional topology of a central-control network such as a passive optical network (PON) or Hybrid fiber coax (HFC) network, prevents each EU from listening to its neighbor""s upstream transmission or monitoring the traffic over the bus or trunk. Therefore, it is difficult to directly implement CSMA/CD over a central-control network unless the CO echoes at least part of the upstream traffic downstream to enable the EUs to monitor the upstream traffic, such as in 10Broad36 Ethernet (See IEEE 802.3). In typical networks with miles of coverage, the large round trip delay is beyond the limitations of the commonly used IEEE 802.3 (Ethernet) standard. Even with certain protocol modifications, this delay will significantly reduce the transmission efficiency.
The invention overcomes the difficulties and limitations associated with Ethernet-like LANs and complexities in reservation based MAC protocols often used in central control systems.
Intermediate nodes (INs) are provided to coordinate local signaling and provide traffic information to each EU without involving the CO. The INs derive traffic information signals from upstream signaling and send the traffic information signals (TIS) downstream to each EU. The INs either generate the TIS or loop back at least a part of the signals or signaling from the EUs. The standard CSMA scheme with Collision Detection or Collision Avoidance (CA) can then be deployed with the help of those INs regardless of whether the original network topology is central-control or peer-to-peer, and independent of CO-EU distance. The intermediate nodes can implement several alternative methods of traffic regulation.
By separating two-way transmission over different communication paths or channels, and enabling two-way operation schemes in the user terminals (i.e. Ethernet cards inside computers), full-duplex transmission can also be achieved with high efficiency and dynamic traffic control. From an operations point of view, the boundary between central control and peer-to-peer control therefore disappears, and customers can use standard Ethernet cards to access the network.